In recent years, hearing aids for hearing-impaired individuals and others who may desire amplified sound to their ear have enjoyed the advance of electronics.
In the past, hearing aids had an ear receiver connected by wires to the sound correction units either behind the ear (BTE) or placed in a pocket or on a belt of the individual. More recently, electronics has become sufficiently miniaturized to permit the entire hearing aid to reside in the ear.
Because the pinna of the ear is the natural sound gathering anatomy for human hearing, the presence of a receiver, amplifier, and transmitter within the pinna and external auditory canal has proven to be an acoustic advantage for the individual. Further, confinement of the ITE hearing aid within the pinna has been viewed as a cosmetic improvement over prior hearing aid constructions.
ITE hearing aids have been produced two ways: (1) a customized fitting to the individual's pinna and/or external auditory canal and (2) a series of stock modular canal aids designed to approximate the pinna and/or external auditory canal of most individuals.
A custom ITE hearing aid is conventionally made using a series of elaborate casting and recasting steps involving more than one visit by the individual to the hearing aid dispenser. A positive ear impression is made of the individual's pinna and external auditory canal which is used to create a negative impression at the hearing aid manufacturer, typically a remote location from the hearing aid dispenser. The negative impression is used to cast a positive impression of the pinna and external auditory canal which is subjected to grinding and polishing steps and assembly of electronic components therein. The assembled ITE hearing aid is returned to the hearing aid dispenser for fitting in the individual's ear. It is common for the fitting process to require several iterations to assure a comfortable fit for the individual. The acoustic fit of the rigid ITE hearing aid through all these casting-fitting operations becomes increasingly inaccurate. More than one individual having undergone the impression and fitting process has not used the hearing aid because of acoustic or structural discomfort.
Stock ITE hearing aids may minimize the number of visits by the individual to the hearing aid dispenser but do not provide an ITE hearing aid which is unique to the individual's pinna and external auditory canal. Thus, both acoustic and comfort fit may suffer.
Others have tried to provide a method for forming hearing aids.
For example, U.S. Pat. No. 3,097,059 (Hoffman) discloses a method for forming in the pinna and external auditory canal a freely moldable mass of soft malleable acrylic resin having placed in its flat external surface a conventional receiver ring for a pocket, hip, or BTE hearing aid. U.S. Pat. No. 3,440,314 (Frisch) also discloses a method of forming a custom-fitted ear plug for a BTE hearing aid using a room temperature curing silicone rubber formed around a tube placed into the external auditory canal.
Methods of forming an ITE hearing aid are disclosed in U.S. Pat. No. 4,091,067 (Kramer et al.) and Voroba, "Hearing Instruments", Vol. 35, No. 1, 1984, pages 12-16. In Kramer et al., a silicone polymer is molded around a small diameter coring form and then pressed into the ear to form a body which conforms to the shape of the pinna and external auditory canal. Thereafter, an apertured component is embedded in the outer surface of the body and, after the composition is cured, the coring form is removed to leave a sound transmitting passageway extending through the receiver and between the apertured component and the ear canal. One embodiment discloses the apertured component to be a miniature speaker acoustically coupled with the sound transmitting passageway. Otherwise, the communications speaker is inserted into the apertured component.
The Voroba article describes the fabrication of a shell using a soft plastic material injected into the ear canal which is molded while an appropriately sized mandrel is pressed into the plastic material. The cavity formed by the mandrel may be fitted with a face plate which snap fits into the cavity and over the distal surface of the shell formed.
With the development of miniature electronic circuits and miniature electronic microphone and receiver transducers, it has become possible to minimize the number of operations needed to determine proper audiology to be used in a hearing aid. For example, Minnesota Mining and Manufacturing Company (3M) markets a hearing aid under the brand "Memory Mate" which uses electronics in the hearing aid to refine through electronic programming the hearing improvement needed for an individual.
It would be preferable for hearing aid dispensers, audiologists, and patients for the currently cumbersome process of preparing a custom fitted hearing aid to be streamlined. A complete, custom hearing aid which could be fitted in one office visit would maximize the convenience of users requiring hearing aids, would compress the time and cost to complete the formation of the hearing aid earmold for acoustical and comfortable fit, and allow completion of the sales transaction in a single visit to the merchant.
Notwithstanding these developments, more recently, methods of making ITE hearing aids have refined
on, positive casting custom process.
For example, U.S. Re. No. 33,017 (U.S. Pat. No. 4,617,429, Bellafiore) uses a dentist's material for making the positive impression, a dental material for making a negative cast, silicone material to cover and preset electronic components which are placed in the negative cavity before filling with acrylic material to mold the final ITE hearing aid.
U.S. Pat. No. 4,834,927 (Birkholz et al.) generates a cavity for electric components to be assembled at a manufacturer by providing a die having an overshell and cap which is inserted into the ear when making the positive impression. The removal of this die, overshell, cap combination provides a negative cavity of a constant dimension into which an electronic ITE module may be seated firmly and acoustically tight.
On the other hand, U.S. Pat. No. 4,871,502 (LeBisch et al.) discloses an otoplastic manufactured directly in the ear by using a die inside a deformable envelope in the ear and the supplying of flowing otoplastic material between the die and the envelope. After the otoplastic has set, die and the envelope are removed and a module of a hearing aid is inserted into the cavity created by the die.
U.S. Pat. No. 4,860,362 (Tweedle) discloses an open end ITE hearing aid shell with a non planar face plate. U.S. Pat. No. 4,870,688 (Voroba et al.) discloses a prefabricated ear shell assembly having a standard fabrication into which electronic components snap fit. The prefabricated shell assembly is a hollow rigid shell with a soft exterior having a cavity into which a variety of electronic components may be tested by the individual at the time of fitting. UK Patent Application 2 203 379 (Painter) discloses inserting a flexible walled membrane into the ear to conform to its surfaces and to serve as the envelope for inserting plastics material to mold to the shape of the ear surfaces. After cure and removal from the ear, the membrane is discarded and the earmold, preferably set in place with a central void, is fitted with an electronics module into the void.
One has disclosed a pre-fabricated hearing aid which may be attempted to be molded in situ in an exterior auditory canal. U.S. Pat. No. 4,712,245 (Lyregaard) discloses the use of a thin elastic layer attached as an envelope around a non-adjustable hearing aid case and sealed at both ends of the case. The space between the envelope and the case is filled with two-component curing ear impression material separated by a thin partitioning wall which can be ruptured under hand pressure to initiate curing. After the appropriate electronics is determined, a stock hearing device with impression material in the envelope is selected. The fitter ruptures the impression material partitioning wall and inserts the device into the ear canal for molding and curing of the impression material within the envelope.
But kneading of the two-part impression material within a confining space between the case and the envelope may not provide an appropriate impression of the pinna and external auditory canal, for Lyregaard emphasizes the ease by which a first fitting may be discarded and replaced by a subsequent fitting(s) using the same process with new component(s). Lyregaard limits the amount of impression material to conform to the convoluted pinna and external auditory canal to that amount contained between the case containing inflexible electronics components and the envelope sealed to the case in order to rely on a stock of modules of electronic components to fit his method of assembly.